polish(v0.7): styled hover tooltips on timeline + push toggle (explain the icon)

Give the two tab-bar line-icon buttons the same styled data-tip hover tooltip as
the toolbar icons, so their meaning is clear on hover (native title was slow/ugly):
- timeline → "Activity timeline"
- push toggle → "Notifications off — tap to turn on" / "…on — tap to turn off"
Left-anchored (they sit on the left of the tab bar). 158 push+tabs tests green.

public/style.css

@@ -1562,3 +1562,33 @@ body.home-open #term {
   font-size: 11px;
   color: var(--text-faint);
 }
+
+/* v0.7: styled hover tooltip on the timeline + push buttons (like .toolbtn).
+   Left-anchored — these sit on the left side of the tab bar. */
+.tab-timeline,
+.push-toggle-btn {
+  position: relative;
+}
+.tab-timeline[data-tip]::after,
+.push-toggle-btn[data-tip]::after {
+  content: attr(data-tip);
+  position: absolute;
+  top: calc(100% + 6px);
+  left: 0;
+  white-space: nowrap;
+  background: var(--surface-3);
+  color: var(--text);
+  border: 1px solid var(--border-strong);
+  padding: 4px 8px;
+  border-radius: 6px;
+  font-size: 12px;
+  font-weight: 500;
+  opacity: 0;
+  pointer-events: none;
+  transition: opacity 0.12s ease;
+  z-index: 60;
+}
+.tab-timeline[data-tip]:hover::after,
+.push-toggle-btn[data-tip]:hover::after {
+  opacity: 1;
+}